This is a proposal to determine by immunological criteria whether the receptor for IgA (FcAlphaR) is distinct from the receptor for IgG (FcGammaR) on human peripheral blood polymorphonuclear leukocytes (PMN). I have previously characterized a mouse monoclonal anti-human neutrophil FcGamma Receptor antibody, which completely inhibited the binding to PMN of IgG coated erythrocytes or soluble IgG immune complexes as well as a rabbit antisera to the PMN Fc Receptor for IgG immune complexes. These immunologic reagents will be used in inhibition experiments, in both soluble and substrate-bound fashion, to determine whether momomeric IgA, secretory IgA, or IgA immune complexes bind to the receptor on PMN which mediates the binding of IgG immune complexes. FcAlphaR and FcGammaR will be quantitated by radiolabeled ligand and by fluorescence activated cell sorter analysis. The FcAlphaR and FcGammaR on PMN isolated from gingival crevices will be quantitated and compared with the number of FcAlphaR and FcGammaR on peripheral blood PMN. These studies, using both immunologic reagents as well as the ligands for these receptors, should provide data to determine whether these plasma membrane proteins on PMN are distinct from one another.